DOCS-2757: update configuration example and reword intro to config file

Signed-off-by: kay <kay.kim@10gen.com>
DOCS-2757: updating cross references

Signed-off-by: kay <kay.kim@10gen.com>
DOCS-3116 ssl options
DOCS-2287 rs.add no longer disconnects shell

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-2287: tweak sentence
trivial: fix versionadded tag to versionchanged
DOCS-2821 cluster uses sslPEMKeyFile if sslClusterFile not specified

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-2821: fixing reference to option
DOCS-2387 new steps format: configure secondary-only member